Signaling system



April 11, 1939. e. c. CUMMINGS SIGNALING SYSTEM Filed March 5, 1958 T AAVA I 2o 19" Ill-@- v :POLAR/ZED" INVENTOR G. C. CUMMINGS A TTOR/VEY Patented Apr. 11, 1939 UNITED STATES PATENT OFFICE SIGNALING SYSTEM Application March .3, 1938, Serial No. 193,649

5 Claims.

This invention relates to signaling means and particularly to electrical telegraph systems wherein a plurality of stations of relatively diiferent importance are connected to a single line.

The object of the invention is to provide relay means responsive to potential changes for operating what is known to those skilled in the art as a hit suppressor circuit. Such. circuit has for its general purpose the provision of means to prevent a station of minor importance from interfering, either through faulty operation or otherwise, with traflic between stations of major importance. Where a main line extending between two stations of major importance has a branch line connected thereto and extending to a station of minor importance, means are provided for artificially blocking out the branch line throughout the period of use of the main line, allowing the branch line to break in at any time but particularly providing for rendering an accidental opening, spoken of as a hit, from being transmitted to the main line.

A feature of the invention is a timing circuit consisting of means for starting the flow of transient currents, such circuit being responsive to open circuit conditions on the branch line for counting time from the start of an open circuit and for maintaining the main line closed for an appropriate period so that a hit will, not be transmitted to the main line. 'If an open circuit condition persists beyond a given period as measured by said transient current timing means, then such open circuit is deemed to be 'a signal and it becomes efiective.

A- further feature of the invention is the use of what might be termed a condenser relay, that is, one which responds to a difference in potential and requires for its operation only that amount of energy which may be measured by the charging current of a small condenser. By way of example, such a relay is shown herein as a piezoelectric crystal relay having a movable element similar in construction and operation to the motor element used by Sawyer in his Reissue Patent No. 20,213, December 22, 1936. In general also, a relay of this nature is shown in the application of Warren P. Mason, Serial No. 131,160, filed March 16, 1937.

The drawing is a circuit diagram illustrating the invention.

There are two stations, I and 2, of major importance, and a third station 3, of minor importance. These are all conventionally illustrated as teletypewriter substation circuits, though the invention is applicable to other systems as well.

The system is arranged so that a hit occurring at station 3 or in line I6 extending between the repeater and station 3 will not interfere with traffic between stations I and 2. Normally, a relay 4 short-circuits the break point in the repeater responsive to station 3 and this relay I is maintained operated just so long as traific is flowing between stations I and 2, and until station 3 makes an effective signal. If a hit should occur on station 3, that is, an open circuit condition of short duration, then means are started to release relay 4 but these means are immediately rendered ineffective by traffic flowing between stations I and 2.

The station I is connected over local loop 5 to a repeater 6 and thence over a long line I to a corresponding repeater including all circuits between line I and line 9 and having a relay 8. In response to code impulses from station I relay 8 is operated and this will reduce the current in line 9 which extends through the contact and armature of relay I0 and thence through the windings of relays II-, I2 and I3 to the armature of relay I4, where it connects to positive battery.

Under normal conditions current flows from negative battery on the armature of relay 8 to positive battery on the armature of relay I4 and consequently, relays I I and I2 are normally energized through their upper windings and in this energized condition have their armatures in positions illustrated. When the sender at station I is operated, each spacing impulse will cause relay 8 to reverse the potential on its armature and thereby operate relays II, I2 and I3. Relay I3 through the movement of its armature will operate the repeater 23 at the end of the line and through it the receiving magnet at station 2. Relay I I, through the movement of its armature, will open the loop I6 to station 3 and cause operation of the receiving magnet thereat. Relay I2 through the movement of its armature causes the current in the upper windings of relays I5 and ID to be reversed so that they will maintain their armatures in the positions shown even though the circuit through their lower windings has been opened at the armature and contact of relay II. In this manner messages may be transmitted from station I to stations 2 and 3 simultaneously and in like manner messages may be transmitted from station 2 to stations I and 3 simultaneously.

When relay I2 operates it armature to its right-hand contact and closes the circuit from positive battery, armature and right-hand contact of relay I2, upper Winding of polar relay I 1 to ground, relay ll moves its armature to its left-hand contact where it may remain even though the upper energizing winding of the relay is opened. Relay I! through its armature and contact short-circuits the condenser I9 and resistance 20 and, therefore, places full ground potential on the middle conducting sheet of condenser type relay l8 and causes a certain current to flow through the resistances 2| and 22 to positive battery. Since the outer conducting sheets of condenser type relay l8 are connected between the resistances 2| and 22, there will be a certain potential difierence between the outer and middle conducting sheets of this relay and it will move its armature to its left-hand contact. This will operate relay 4 and relay 4 in turn will short-circuit the contacts of relay Ill. Normally these contacts are operated by spacing impulses or other open circuit conditions at station 3 but so long as relay 4 is operated, the open circuit caused by relay I is ineffective and can cause no interference with traffic between stations I and 2. Should such an open circuit occur, it would under normal conditions cause the operation of relays l6 and I and relay IS in establishing a circuit from negative battery, its armature contact and thence through the lower winding of polar relay ll, would cause the movement of the armature of relay I! toits right-hand contact. If such open circuit condition is of only short duration then any impulses coming over the main line and operating relay l2 would cause the immediate restoration of relay ll to its left-hand contact. If such open circuit condition, however, is of longer duration, the relay i5 renders relays II and I2 ineffective and hence relay I! will remain as shown. When armature of relay I1 is moved off its left-hand contact, condenser i9 starts to charge from ground on one terminal to positive battery through resistances 29, 2| and 22. The constants of condenser l9 and resistances 29 to 22 inclusive, are such that the transient charging current on condenser I9 is maintained for a period somewhat longer than a normal spacing impulse and during the flow of this transient current the potential diiference across the crystals of a condenser type relay i8 is maintained sufficiently high to keep this relay operated. Any spacing impulse sent between stations 1 and 2 during this period will, if relay i5 has returned to the position shown, move relay I! to its left contact and reestablish the full potential difference across the terminals of relay l8 and thus maintain relay 4 operated.

Station 3 may break in by sending a spacing impulse and operating relay I5 which will move the armature of relay [1 to its right contact. After a period timed by the transient current timing circuit comprising condenser 19 and resistances 20 to 22 inclusive, relay 4 will be released and spacing impulses sent by station 3 will be transmitted to both stations I and 2.

What is claimed is:

1. A signaling system comprising a plurality of stations of major and minor importance, a common line for said stations, a repeater in said line forming a junction point between branches extending to stations of major importance and a station of minor importance, means in said repeater for blocking the said branch extending to said station of minor importance, means responsive to signals transmitted by stations of major importance for operating said first means, means responsive to signals transmitted by said station of minor importance for releasing said first means, said first means including a condenser type relay responsive to a difference in potential and requiring for its operation only that amount of energy which may be measured by the operating current of a small condenser.

2. A signaling system as claimed in claim 1, wherein a piezoelectric crystal is employed as the moving element in said condenser type relay.

3. A signaling system as claimed in claim 1, wherein a Rochelle salt crystal is employed as the moving element in said condenser type relay.

4. A signaling system comprising a plurality of stations of major and minor importance, a common line for said stations, a repeater in said line forming a junction point between branches extending to stations of major importance and a station of minor importance, means in said repeater for blocking said branch extending to said station of minor importance, means responsive to signals transmitted by said stations of major importance for operating said first means,

means responsive to signals transmitted by said station of minor importance for releasing said first means, said first means including a condenser type relay and a circuit responsive to a signal from said station of minor importance for starting the flow of transient currents therein and at the termination thereof for establishing a potential sufficient to operate said condenser type relay, the constants of said circuit being so arranged that said potential will be established only after an interval equal to a signal of unusual length.

5.'A signaling system comprising a plurality of stations, a line connecting said stations, a repeater in said line forming a junction point for a branch line, means responsive to signals from other stations for normally blocking said branch line, means responsive to a prolonged open circuit condition on said branch line for releasing said blocking means, said releasing means including a transient current timing circuit constructed and arranged to establish a potential difference after an interval sufi'iciently long to be marked as a pro-longed open circuit condition, and a condenser type relay responsive thereto.

GEORGE C. CUMMINGS. 

